Easily produced circuits are desirable for many electronic applications. The costs of the production are of great importance.
Existing techniques for the manufacture of such circuits have made it possible to produce many different structures.
Thus, for example, it is possible to produce circuits with the aid of Thin-film Organic and inorganic Large Area Electronic (TOLAE) techniques, but these structures are often inadequate in regard to their high-frequency properties, so that a use at high frequencies is often not possible. This is due to the fact, for example, that the process temperatures have to be kept relatively low, e.g., in order to obtain mechanically flexible substrates, and so the structural/electronic quality of the thin semiconductor films is poor as compared to classical semiconductor substrates or materials with high crystallinity.
In particular, the cost-effective production of thin-film Schottky diodes having corresponding high-frequency properties beyond 20 MHz of the typical diode characteristic has been extremely difficult thus far.
Given this situation, one problem which the invention proposes to solve is to provide a method for the production of components having a Schottky diode which makes it possible to produce the corresponding components with the corresponding high-frequency properties in a cost-effective manner.
The problem is solved by a method according to claim 1. Further advantageous embodiments are the subject matter in particular of the dependent claims. Moreover, the problem is solved by components according to claim 3 which are produced by one of the methods.
Insofar as reference is made below to particular reference symbols, these are generally meant to apply equally to all representations, unless otherwise specified.
Furthermore, insofar as hatchmarks or other graphical means are used in the figures, unless otherwise specified the same or an equivalent element is represented with the same hatchmarks or graphical means.
According to a method per the invention, components having a Schottky diode are produced by means of printing technology.
This makes use of a substrate S, as shown for example in FIG. 4. The substrate S may optionally be provided in advance in a step 50 with a bonding layer depending on its properties in regard to a bonding with a subsequently applied electrode E1. Such techniques are known in the prior art and may involve for example the laminating of a heat-stable polymer substrate. Alternatively, however, step 50 may also be used to apply a polymer substrate as a self-standing substrate, which may be stripped off from the carrier substrate S after the processing according to the invention, e.g., in order to enable mechanically flexible circuits.
Next, in a further step 75, the electrode E1 may be applied by means of known techniques. Such techniques are, for example, printing and/or PVD (Physical Vapor Deposition). The electrode E1 may be formed by means of masks M1 or afterwards by means of lithography. The semifinished part so obtained can then be further processed.
Now, in a step 100, a semiconductor-nanoparticle dispersion HND is applied to and deposited on the first electrode E1. Doctor blade techniques, silk screen methods, ink jet printing, rotational coating and the like may be used, or the dispersion is poured out.
After this, laser light L is beamed onto the thin film obtained from the deposited semiconductor-nanoparticle dispersion HND in step 200 to form a mu-cone C1 from the semiconductor-nanoparticle dispersion HND. The height and thickness of a mu-cone or a plurality of mu-cones can be adjusted, e.g., by the thickness of the thin film obtained from the semiconductor-nanoparticle dispersion HND, the energy/power density of the (pulsed) laser light L, the pulse frequency of the laser light L (if any), the scanning rate of the laser light L, the oxide fraction in the semiconductor-nanoparticle dispersion HND, or through the surface energy of the electrode E1.
Advantageously, the electrode E1 is designed so as to withstand a laser treatment. The intensity and application time of the laser light L are important, accordingly. Typically, the choice of material (melting point) as well as the design of the electrode (thickness, area, thermal capacity) itself can ensure that the material of the electrode E1 withstands the laser treatment. Examples of electrode materials are titanium but also gold, silver, copper or aluminum.
Although in the following only one mu-cone shall be discussed, it is obvious to the person skilled in the art that a plurality of mu-cones C1, C2, . . . Cn may be produced in parallel and/or sequentially by means of one or more laser light sources L from the same deposited semiconductor-nanoparticle dispersion HND. Of course, a different semiconductor-nanoparticle dispersion HND may also be applied, from which mu-cones Cn+1, Cn+2, . . . Cn+m may be formed in turn. In this case, the previous thin film obtained from the semiconductor-nanoparticle dispersion HND that was not used for the forming of mu-cones C1, C2, . . . Cn can remain on the substrate S/electrode E1 or be removed, depending on the application.
The removal of [a] deposited semiconductor-nanoparticle dispersion HND which was not used for the forming of mu-cones C1, C2, . . . Cn, Cn+1, Cn+2, . . . Cn+m may involve a flow off and/or other cleaning steps, such as blow off, rinse off, undercut etching, etc.
Now one or more mu-cones C1, C2, . . . Cn, Cn+1, Cn+2, . . . Cn+m are formed, each one having a bottom and a tip, wherein the bottom of a mu-cone C1, C2, . . . Cn, Cn+1, Cn+2, . . . Cn+m is connected to the first electrode E1.
In a further step 300, the mu-cone C1 or the mu-cones C1, C2, . . . Cn, Cn+1, Cn+2, . . . Cn+m so formed are embedded in an electrically insulating polymer matrix P.
The polymer matrix P may comprise at least one of the group of acrylic acid esters, polyurethanes, silicones or epoxy resins, such as polyimides, polycarbonates, and/or polyacrylates.
The polymer matrix P may be cross-linked or not. If a cross-linking is desired, e.g., on account of a better supporting effect, better stability, and/or better electrical properties (e.g., insulating properties), etc., the polymer matrix may be cross-linked by activation (e.g., by means of UV light or laser light L) or undergo excitation for the cross-linking.
Depending on the thickness of the polymer matrix P, it may optionally be necessary to re-expose the tips of the mu-cone C1 or the mu-cones C1, C2, . . . Cn, Cn+1, Cn+2, . . . Cn+m in a step 400. This may be done for example by means of suitable etching methods, such as Reactive Ion Etching (RIE) possibly with addition of suitable process gases, such as oxygen and/or CF4 and/or SF6.
Once the tips of the mu-cone C1 of the mu-cones C1, C2, . . . Cn, Cn+1, Cn+2, . . . Cn+m are exposed, a second electrode E2 may be deposited in a further step 500, so that the tips of the mu-cone C1 or the mu-cones C1, C2, . . . Cn, Cn+1, Cn+2, . . . Cn+m are connected to the second electrode E2.
Although only one second electrode E2 is described above, of course this may also involve a plurality of electrodes just as with the first electrode E1. For example, mu-cones which have been formed from a first semiconductor-nanoparticle dispersion HND may be connected to another electrode as mu-cones which have been formed from another semiconductor-nanoparticle dispersion HND.
The second electrode can be made of the most diverse materials. The methods of applying the second electrode may be correspondingly different as well.
Thus, the second electrode E2 may likewise be applied by means of PVD methods and/or printing as described above in step 75.
Since the second electrode E2 is generally no longer processed by laser, the range of possible materials is significantly larger. Thus, besides the classical metallic and metal oxide electrodes, one may also use electrically conductive polymers such as poly-3,4-ethylene dioxythiophene, doped polyacetylene, spiro, as well as graphene or fullerene.
Therefore, the Schottky barrier between the second electrode E2 and the mu-cone C1 or the mu-cones C1, C2, . . . Cn, Cn+1, Cn+2, . . . Cn+m can be influenced by means of suitable choice of material and processing method. This can be achieved, e.g., by targeted modification of the mu-cone tips (oxide/no oxide, lattice modifications, polymer functionalization).
Thus, e.g., a formation of oxide on the tips of the mu-cones can be encouraged, for example, by a (local) heat treatment in oxygen-rich atmosphere. Furthermore, it is possible to form oxide on the tips of the mu-cones simply by the fact that, for example, nanoparticles are already (partly) oxidized prior to the laser light exposure in step 200. But oxides can also be removed by treatment with HF (hydrofluoric acid) or the like. Lattice defects at the tips of the mu-cones may be introduced for example by means of sputter etching (ion etching).
Thus, with the methods of the invention as described above, components having a Schottky diode can be manufactured. The components comprise at least one mu-cone C1; C2 with a bottom and a tip, with the mu-cone C1; C2 comprising semiconductor material. The mu-cone C1; C2 is embedded in an electrically insulating polymer matrix P, while the bottom of the mu-cone C1; C2 is connected to a first electrode E1 on the side of a substrate and the tip of the mu-cone C1; C2 is connected to a second electrode E2. Either the first electrode E1 or the second electrode E2 forms a Schottky contact SC with the mu-cone C1; C2, while the respective other electrode E2; E1 forms a substantially ohmic contact OC.
Several such components are shown in cross section in FIG. 1. An equivalent electrical circuit is represented in FIG. 2.
In FIGS. 1, 2 and 3 it is assumed that the tip of the mu-cone C1; C2 forms a Schottky contact SC with the second electrode E2 in each case, while the bottom of the mu-cone C1; C2 forms a substantially ohmic contact OC with the first electrode E1. The equivalent electrical circuit of an individual mu-cone according to embodiments of the invention is represented in FIG. 3.
In particular, the invention makes it possible for the semiconductor in the semiconductor-nanoparticle dispersion HND to be of any given type of doping, e.g., p-doped, n-doped or even undoped.
Accordingly, as also described above, different semiconductor-nanoparticle dispersions HND with different dopings may be used in succession, as described above.
In particular, the semiconductor in the semiconductor-nanoparticle dispersion HND may comprise Si, Se, Ge or a III-V semiconductor, such as InP, GaAs, etc.
With the aid of the invention indicated above, it is possible in particular to process even flexible substrates S. Flexible substrates S may be, for example, polymer film, flexible printed circuit boards, paperlike materials, as well as textile substrates. But inflexible materials such as wafers may also be used as substrates S.
Thus, with the help of the invention, it is possible to produce components having a Schottky diode with cost-effective printable thin-film methods which have the required electrical properties of typical diode characteristics even in high-frequency applications. This is achieved in particular in that it is now possible to produce crystalline diodes with the aid of the technique of the invention. The term crystalline should not be understood in a limiting sense with regard to the invention, and it also encompasses polycrystalline or microcrystalline mu-cones. Furthermore, the invention also makes possible the production of amorphous mu-cones in the same way.
In particular, Schottky diodes with typical diode characteristics not only at 20 MHz or more but also reaching into the GHz range (>1 GHz, especially 2 GHz, and preferably >10 GHz) can be realized in cost-effective manner by means of cost-effective techniques.